Pharmaceutical compounds

ABSTRACT

Piperazine derivatives of the formula ##STR1## their esters and salts are useful as modulators of multiple drug resistance.

The present invention relates to compounds useful as modulators ofmultiple drug resistance (MDR), to their preparation and topharmaceutical and veterinary compositions containing them.

The resistance of tumours to treatment with certain cytotoxic agents isan obstacle to the successful chemotherapeutic treatment of cancerpatients. A tumour may acquire resistance to a cytotoxic agent used in aprevious treatment. A tumour may also manifest intrinsic resistance, orcross-resistance, to a cytotoxic agent to which it has not previouslybeen exposed, that agent being unrelated by structure or mechanism ofact on to any agent used in previous treatments of the tumour.

Analogously, certain pathogens may acquire resistance to pharmaceuticalagents used in previous treatments of the diseases or disorders to whichthose pathogens give rise. Pathogens may also manifest intrinsicresistance, or cross resistance, to pharmaceutical agents to which theyhave not previously been exposed. Examples of this effect includemulti-drug resistant forms of malaria, tuberculosis, leishmaniasis andamoebic dysentery.

The above phenomena are referred to collectively as multi-drugresistance (MDR). As discussed more fully later on, a plasma membraneglycoprotein (P-gp) is implicated in the mechanism which underlies MDR.P-gp has drug binding properties. Certain agents which have the capacityto modulate MDR may therefore also be useful in facilitating thedelivery of drugs across the blood-brain barrier and in treating AIDSand AIDS-related complex.

Disadvantages of drugs which have so far been used to modulate MDR,termed resistance modifying agents or RMAs, are that they frequentlypossess a poor pharmacokinetic profile and/or are toxic at theconcentrations required for MDR modulation.

It has now been found that a series of diketopiperazine derivatives haveactivity as modulators of multiple drug resistance. The presentinvention therefore provides a piperazine of general formula (A):##STR2## wherein denotes an optional bond, provided that both ##STR3##and ##STR4## are bonds and ##STR5## and ##STR6## are not bonds, or both##STR7## and ##STR8## are bonds and ##STR9## and ##STR10## are notbonds; X and Y, which may be the same or different, are independentlyselected from

(i) a heterocyclic ring selected from furan, thiophene, pyridine andindole, the indole ring being optionally N-substituted byphthalimidyl-C₁ -C₆ -alkyl, succinimidyl-C₁ -C₆ -alkyl, oxo- ordioxo-indolenyl, --(CH₂)_(n) COOR₁₁, or --(CH₂)_(n) COOCH₂ Ph, whereinR₁₁ is H or C₁ -C₆ alkyl and n is 0, 1 or 2;

(ii) a phenyl ring which is unsubstituted or substituted by one or moresubstituents selected from halogen, C₁ -C₆ alkoxy, --NO₂ and NR₁₁ R₁₂wherein R₁₁ and R₁₂ are each, independently, H or C₁ -C₆ alkyl;

(iii) a cyclohexyl group; and

(iv) a group --CH═C(R₁₇)(Ar);

R₁₇ is H or optionally substituted phenyl and Ar is optionallysubstituted phenyl, the optional substituents on the phenyl ring in eachcase being selected from halogen, --NO₂, --N(R₁₁ R₁₂) wherein R₁₁ andR₁₂ are as defined above and C₁ -C₆ alkoxy;

R₁₄ is H or C₁ -C₆ alkyl optionally substituted by phenyl;

R₁₅ is H or C₁ -C₆ alkyl, optionally substituted by an N-phthalimidyl,N-succinimidyl or oxo- or dioxo-indolenyl group and

R₁₆ is C₁ -C₆ alkyl optionally substituted by an N-phthalimidyl,N-succinimidyl or oxo- or dioxo-indolenyl group;

with the proviso that

(a) X and Y are not both a phenyl ring as defined above under (ii), and

(b) when ##STR11## and ##STR12## are both bonds at least one of R₁₄ andR₁₅ is other than hydrogen;

or a pharmaceutically acceptable salt or ester thereof.

In one embodiment the piperazine is of the following formula (Aa):##STR13## wherein R₁₄, R₁₅, X and Y are as defined above.

In another embodiment the piperazine is of the following formula (Ab):##STR14## wherein R₁₄, R₁₆, X and Y are as defined above.

When either X or Y is a substituted phenyl ring, the benzene ring may besubstituted at any of the ortho, meta and para positions by one or moresubstituents, for example one, two or three substituents, which may bethe same or different, independently selected from the groups specifiedunder (ii) above.

An alkyl group may be linear or branched, or may comprise a cycloalkylgroup. A C₁ -C₆ alkyl group is typically a C₁ -C₄ alkyl group, forexample a methyl, ethyl, propyl, i-propyl, n-butyl, sec-butyl,tert-butyl or cyclopropylmethyl group. A halogen is, for example,fluorine, chlorine, bromine or iodine. A C₁ -C₆ alkyl group substitutedby halogen may be substituted by 1, 2 or 3 halogen atoms. It may be aperhaloalkyl group, for example trifluoromethyl.

A C₁ -C₆ alkoxy group is typically a C₁ -C₄ alkoxy group, for example amethoxy, ethoxy, propoxy, i-propoxy, n-butoxy, sec-butoxy or tert-butoxygroup.

In compounds of formula A free rotation may occur at room temperatureabout the single bonds connecting X and Y to the double bonds atpositions 3 and 6 of the 2,5-piperazinedione ring. When either of X andY is a phenyl group, therefore, positions 2 and 6, and positions 3 and5, in both benzene rings can therefore be considered as equivalent.

When ##STR15## and ##STR16## are bonds in formula A at least one of R₁₄and R₁₅ is other than hydrogen. When R₁₄ and R₁₅ are both C₁ -C₆ alkylthey may be the same or different. Preferred C₁ -C₆ alkyl groups for R₁₄and R₁₅ are Me, Et and cyclopropylmethyl. For example R₁₄ is C₁ -C₆alkyl and R₁₅ is H or C₁ -C₆ alkyl, or R₁₅ is C₁ -C₆ alkyl and R₁₄ is Hor C₁ -C₆ alkyl. In one embodiment R₁₄ is Me, Et or cyclopropylmethyland R₁₅ is H, Me, Et or cyclopropylmethyl. In a second embodiment R₁₅ isMe, Et or cyclopropylmethyl and R₁₄ is H, Me, Et or cyclopropylmethyl.

When ##STR17## and ##STR18## are both bonds in formula A, R₁₆ is C₁ -C₆alkyl optionally substituted by an N-phthalimidyl group and R₁₄ is H orC₁ -C₆ alkyl, optionally substituted by phenyl. Typically R₁₄ or H isMe, Et or cyclopropylmethyl.

When X or Y is a phenyl ring it may be unsubstituted or mono-substitutedat any one of positions 2 to 6 in the benzene ring. The benzene ring mayinstead be 2,3-, 2,4-, 2,5-, 2,6-, 3,4- or 3,5- disubstituted, or2,3,4-, 2,3,5-, 2,3,6- or 3,4,5-trisubstituted.

In one embodiment one of X and Y is an unsubstituted or substitutedphenyl ring and the other is a heterocyclic ring, a cyclohexyl group ora group --CH═CHPh or --CH═CH(Ph)₂. Preferred examples of a heterocyclicring include a 4-pyridyl, furan-2-yl, furan-3-yl, thiophen-2-yl andoptionally substituted indol-3-yl group.

In another embodiment R₁₆ is a phthalimidyl-C₁ -C₆ alkyl group and Y isan optionally N-substituted indole ring.

In a third embodiment R₁₄ is C₁ -C₆ alkyl substituted by phenyl and Y isa pyridine ring.

Certain diketopiperazines have been disclosed as having utility asbioactive agents. Yokoi et al in J. Antibiotics vol XLI No. 4, pp494-501 (1988) describe structure-cytotoxicity relationship studies on aseries of diketopiperazines related to neihumicin, a compound obtainedfrom the micro-organism Micromonospora neihuensis. Kamei et al in J.Antibiotics vol XLIII No. 8, 1018-1020 disclose that twodiketopiperazines, designated piperafizines A and B, have utility aspotentiators of the cytotoxicity of vincristine.

Examples of specific compounds of the invention are as follows. Thecompound numbering is adhered to in the rest of the specification:

1894(3Z,6Z)-6-Benzylidene-1-methyl-3-(1-tert-butoxycarbonyl-3-(l-tert-butoxycarbonyl-3-indolyl)methylene-2,5-piperazinedione.

1895(3Z,6Z)-6-Benzylidene-1-methyl-5-(3-phthalimidopropoxy)-3-(l-tert-butoxycarbonyl-3-indolyl)methylene-3,6-dihydro-2-pyrazinone.

1899(37)-1-Acetyl-3-benzylidene-5-(3-phthalimidopropoxy)-1,2,3,6-tetrahydro-2-pyrazinone.

1855(3Z,6Z)-3,6-Dibenzylidene-1-methyl-5-pentyloxy-3,6-dihydro-2-pyrazinone.

1840(3Z,6Z)-1-Benzyl-6-benzylidene-3-(4-pyridyl)methylene-2,5-hydrochloride.

1834(3Z,6Z)-1,4-Dimethyl-3-(1-tert-butoxycarbonyl-3-indolyl)methylene-6-(2-thenylidene)-2,5-piperazinedione.

1839(3Z,6Z)-1-Benzyl-6-benzylidene-3-(4-pyridyl)methylene-2,5-piperazinedione.

1932(3Z,6Z)-3,6-Dibenzylidene-4-methyl-1-(3-succinimidopropyl)-2,5-piperazinedione.

1934(3Z,6Z)-3,6-Dibenzylidene-1-methyl-5-(3-succinmidopropoxy)-3,6-dihydro-2-pyrazinone.

1942(3Z,6Z)-3-Benzylidene-1,4-dimethyl-6-(1-tert-butoxycarbonyl)-3-indolyl)methylene-2,5-piperazinedione.

1943(3Z,6Z)-3-Benzylidene-1,4-dimethyl-6-(3-(1-(3-phthalimido)propyl)indolyl)methylene-2,5-piperazinedione.

1941(3Z,6Z)-3-Benzylidene-6-1-methoxycarbonyl-3-indolyl)methylene-1,4-dimethyl-2,5-piperazinedione.

1940(3Z,6Z)-3-Benzylidene-6-(1-benzyloxycarbonyl-3-indolyl)methylene-1,4-dimethyl-2,5-piperazinedione.

1935(3Z,6Z)-3,6-Dibenzylidene-5-(2,3-dioxo-1-indolinyl)propoxy-1-methyl-3,6-dihydro-2-pyrazinone.

1937(3Z,6Z)-3-Benzylidene-1,4-dimethyl-6-(γ-phenylcinnamylidene)-2,5-piperazinedione.

1800(3Z,6Z)-3-Benzylidene-1,4-dimethyl-6-(1-tert-butoxycarbonyl-3-indolyl)methylene-2,5-piperazinedione.

1947(3Z,6Z)-3,6-Di-(3-(2-dimethylaminoethoxy)benzylidene)-2,5-piperazinedione.

1596(3Z,6Z)-6-(3-furylmethylene)-3-(4-methoxybenzylidene-1-methyl-2,5-piperazinedione.

1938(3Z,6Z)-3-Benzylidene-6-(4-dimethylaminobenzylidene)-1,4-dimethyl-2,5-piperazinedione.

1933(3Z,6Z)-6-Benzylidene-3-cyclohexylmethylene-1-methyl-2,5-piperazinedione.

1799 (3Z,6Z)-3-Benzylidene-6-(2-furyl)-1,4-dimethyl-2,5-piperazinedione.

1896(3Z,6Z)-3-Benzylidene-6-(3-indoly)methylene-1,4-dimethyl-2,5-piperazinedione.

1597(3Z,6Z)-3-(4-Methoxybenzylidene)-1-methyl-6-(2-thienylmethylene)-2,5-piperazinedione.

1641(3Z,6Z)-3-Benzylidene-1-methyl-6-(3-thienylmethylene)-2,5-piperazinedione.

1771(3Z,6Z)-3,6-Dibenzylidene-5-methoxy-1-methyl-3,6-dihydro-2-pyrazinone.

1570(3Z,6Z)-6-Benzylidene-5-methoxy-3-(2-thenylidene)-3,6-dihydro-2(1H)-pyrazinone.

1563(3Z,6Z)-3-(3-Furyl)methylene-6-(4-methoxybenzylidene)-1-methyl-2,5-piperazinedione.

1565(3Z,6Z)-6-(4-Methoxybenzylidene)-1-methyl-3-(1-tert-butoxycarbonyl-3-indolyl)methylene-2,5-piperazinedione.

1777(3Z,6Z)-3-Cinnamylidene-6-(4-methoxybenzylidene)-1,4-dimethyl-2,5-piperazinedione.

1836(3Z,6Z)-6-Benzylidene-3-furylidene-1,4-dimethyl-2,5-piperazinedione.

1871(3Z,6Z)-3-Benzylidene-6-cyclohexylmethylene-1,4-dimethyl-2,5-piperazinedione.

1873(3Z,6Z)-6-(2,6-dichlorobenzylidene)-3-(1-tertbutoxycarbonyl-3-indolyl)methylene-1,4-dimethyl-2,5-piperazinedione.

1874(3Z,6Z)-4-benzyl-3-(1-tertbutoxycarbonyl-3-indolyl)methylene-6-(4-methoxybenzylidene)-1-methyl-2,5-piperazinedione.

1875(3Z,6Z)-6-(3-furylmethylene)-6-(1-tertbutoxycarbonyl-3-indolyl)methylene-1,4-dimethyl-2,5-piperazinedione.

1877(3Z,6Z)-1,4-dimethyl-6-(2-nitrobenzylidene)-3-(2-thienylmethylene)-2,5-piperazinedione.

1880(3Z,6Z)-4-Benzyl-3-(3-furylmethylene)-6-(4-methoxybenzylidene)-1-methyl-2,5-piperazinedione.

1563(3Z,6Z)-3-(3-Furylmethylene)-6-(4-methoxybenzylidene)-1-methyl-2,5-piperazinedione.

1564(3Z,6Z)-6-(4-Methoxybenzylidene)-1-methyl-3-(2-thienylmethylene)-2,5-piperazinedione.

1569(3Z,6Z)-3-Benzylidene-1-methyl-6-(2-thienylmethylene)-2,5-piperazinedione.

Compounds of formula A may be prepared by a process which compriseseither (a) condensing a compound of formula (I): ##STR19## wherein R₁₅and Y are as defined above and are optionally protected, with a compoundof formula (II): ##STR20## wherein X is as defined above and isoptionally protected, in the presence of a base in an organic solvent,thereby obtaining a compound of formula A in which R₁₄ is hydrogen; or(ii) condensing a compound of formula (I'): ##STR21## wherein R₁₄ and Xare as defined above and are optionally protected, with a compound offormula (III): ##STR22## wherein Y is as defined above and is optionallyprotected, in the presence of a base in an organic solvent, therebyobtaining a compound of formula A in which R₁₅ is hydrogen; and, ineither case (i) or (ii), if desired, converting the resulting compoundof formula A in which R₁₄ or R₁₅, respectively, is hydrogen into acorresponding compound of formula A in which R₁₄ and R₁₅, respectively,is a C₁ -C₆ alkyl group, by treatment with an alkylating agent offormula R₁₄ --X or R₁₅ --X wherein R₁₄ and R₁₅ are as defined above andX is halogen; or, if desired, converting a compound of formula A inwhich R₁₅ is hydrogen into a compound of formula A wherein R₁₆ is asdefined above, by treatment with an alkylating agent of formula R₁₆ --Xwherein R₁₆ is as defined above and X is a halogen, and/or if required,removing optionally present protecting groups and/or, if desired,converting one compound of formula A into another compound of formula A,and/or, if desired, converting a compound of formula A into apharmaceutically acceptable salt or ester thereof, and/or, if desired,converting a salt or ester into a free compound, and/or, if desired,separating a mixture of isomers of compounds of formula A into thesingle isomers.

The process can give rise to a mixture of O-alkylated and N-alkylatedproducts, i.e. a mixture of compounds of formula (Aa) and (Ab), asdefined above, wherein R₁₅ and R₁₆ are the same. The relativeproportions of the two products will vary depending on the nature of R₁₅and R₁₆, which determines in turn the relative extent of N-alkylationcompared to O-alkylation. The two may be separated by conventionalmethods, for example column chromatography, and obtained separately.

A compound of formula A produced directly by the condensation reactionbetween (I) and (II) or (I') and (III) may be modified, if desired, byconverting optional substituents on groups X and Y into othersubstituents. These optional conversions may be carried out by methodsknown in themselves. For example, a compound of formula A in which X orY is an indolyl group may be converted into a compound of formula Awherein the imidazoyl group is N-substituted by treatment with anappropriately substituted halide such as benzyl haloformate, ahaloalkylphthalimide or an alkylhaloacetate, for instance in DMSO atroom temperature.

A compound of formula A in which one of X and Y is a phenyl groupsubstituted by an NO₂ group may be converted into a compound of formulaA in which one of X and Y is a phenyl group substituted by an aminogroup N(R₁₁ R₁₂) by reduction under standard conditions, for example bycatalytic hydrogenation.

Protecting groups for substituents on X or Y in any of the compounds offormulae (I), (I'), (II) and (III) are optionally introduced prior tostep (i) or step (ii) when any of those substituents are groups whichare sensitive to the condensation reaction conditions or incompatiblewith the condensation reaction, for example an amino group. Theprotecting groups are then removed at the end of the process. Anyconventional protecting group suitable for the group in question may beemployed, and may be introduced and subsequently removed by well-knownstandard methods.

The condensation reaction between compounds (I) and (II) or (I') and(III) is suitably performed in the presence of a base which is potassiumt-butoxide, sodium hydride, potassium carbonate, sodium carbonate,caesium carbonate, sodium acetate, potassium fluoride on alumina, ortriethylamine in a solvent such as dimethylformamide, or in the presenceof potassium t-butoxide in t-butanol or a mixture of t-butanol anddimethylformamide. The reaction is typically performed at a temperaturefrom 0° C. to the reflux temperature of the solvent.

The alkylation of a compound of formula A wherein R₁₄ or R₁₅ is H iscarried out using an appropriate conventional alkylating agent such as ahaloalkane, for example an iodoalkane, or a dialkylsulphate, in thepresence of a base in an organic solvent. The base may be, for example,sodium hydride, sodium carbonate or potassium carbonate. A suitablesolvent is then DMF. Another suitable base is aqueous sodium hydroxide,in which case a suitable cosolvent is, for example, dioxan, THF or DMF.

The compounds of formula (I) may be prepared by a process comprisingreacting 1,4-diacetyl-2,5-piperazinedione with a compound of formula(III) as defined above, in the presence of a base in an organic solvent,thereby obtaining a compound of formula (I) wherein R₁₅ is hydrogen;and, if desired, treating the resulting compound of formula (I) with analkylating agent to obtain a compound of formula (I) in which R₁₅ is aC₁ -C₆ alkyl group. Similarly, the compounds of formula (I') may beprepared by a process which comprises reacting1,4-diacetyl-2,5-piperazinedione with a compound of formula (II) asdefined above, in the presence of a base in an organic solvent, therebyobtaining a compound of formula (I') in which R₁₄ is hydrogen; and, ifdesired, treating the resulting compound of formula (I') with analkylating agent to obtain a compound of formula (I') in which R₁₄ is aC₁ -C₆ alkyl group.

If necessary, the resulting compound of formula (I) or (I') can beseparated from other reaction products by chromatography.

The reaction of 1,4-diacetyl-2,5-piperazinedione with the compound offormula (III) or (II) is suitably performed under the same conditions asdescribed above for the condensation between compounds (I) and (II), or(I') and (III).

The alkylation of a compound of formula (I) in which R₁₅ is hydrogen, ora compound of formula (I') in which R₁₄ is hydrogen, is suitably carriedout using the same conventional alkylating agents and under the sameconditions as described above for the alkylation of compounds of formula(A) in which R₁₄ is hydrogen. The alkylation step in the case of acompound (I) where R₁₅ is hydrogen typically gives rise to a mixture ofthe compound of formula (I) in which R₁₅ is a C₁ -C₆ alkyl group and itsisomer of the following formula (IV) in which R₁₅ is a C₁ -C₆ alkylgroup: ##STR23##

The alkylation step in the case of a compound (I') where R₁₄ is hydrogentypically gives rise to a mixture of the compound of formula (I') whereR₁₄ is a C₁ -C₆ alkyl group and its isomer of formula (IV') where R₁₄ isa C₁ -C₆ alkyl group: ##STR24##

The mixture of compounds (I) and (IV), where R₁₅ is other than hydrogen,or compounds (I') and (IV'), where R₁₄ is other than hydrogen, canreadily be separated by chromatography, for example on silica gel.Suitable eluants include ethyl acetate and hexane, or methanol anddichloromethane.

The substituted benzaldehydes of formulae (II) and (III) are knowncompounds or can be prepared from readily available starting materialsby conventional methods. The 1,4-diacetyl-2,5-piperazinedione used as astarting material in the preparation of compounds of formula (I) may beprepared by treating 2,5-piperazinedione (glycine anhydride) with anacetylating agent. The acetylation may be performed using anyconventional acetylating agent, for example acetic anhydride underreflux or, alternatively, acetic anhydride at a temperature below refluxin the presence of 4-dimethylaminopyridine.

Compounds of formula (I) wherein R₁₅ is H may also be prepared by themicrowave irradiation of a mixture comprising1,4-diacetyl-2,5-piperazinedione, a compound of formula (III) andpotassium fluoride on alumina (as base) in the absence of solvent.

Compounds of formula (I) wherein R₁₅ is H may alternatively be prepareddirectly from 2,5-piperazinedione (glycine anhydride) by a process whichcomprises treating the 2,5-piperazinedione with a mixture comprising acompound of formula (III), sodium acetate and acetic anhydride at anelevated temperature, for example under reflux.

Compounds of formula (I') wherein R₁₄ is H may be prepared by analogousprocesses, replacing compound (III) in each case by a compound offormula (II).

Compounds of formula A may also be prepared by a process comprising themicrowave irradiation of (i) a mixture comprising a compound of formula(I) as defined above wherein R₁₅ is H or C₁ -C₆ alkyl, a compound offormula (II) and potassium fluoride on alumina, or (ii) a mixturecomprising a compound of formula (I') wherein R₁₄ is H or C₁ -C₆ alkyl acompound of formula (III) and potassium fluoride on alumina, or (iii) amixture comprising 1,4-diacetylpiperazine-2,5-dione, a compound offormula (II), a compound of formula (III) and potassium fluoride onalumina. The irradiation is performed in the absence of a solvent. Theresulting compound in which R₁₄ and R₁₅ are both H may then be alkylatedusing an appropriate alkylating agent, for example as described above.

Compounds of formula A may also be obtained directly by a process whichcomprises condensing together 1,4-diacetyl-2,5-piperazinedione, acompound of formula (II) and a compound of formula (III) in the presenceof a base in an organic solvent. Suitable bases, solvents and reactionconditions are as described above for the condensation reaction between,for example, compounds (I) and (II).

An alternative direct process for the preparation of compounds offormula A comprises condensing together 2,5-piperazinedione, a compoundof formula (II) and a compound of formula (III) in the presence ofsodium acetate and acetic anhydride at elevated temperature, for exampleunder reflux.

An alternative process for the preparation of compounds of formula (I)comprises treating a compound of formula (V): ##STR25## wherein R₆ toR₁₀ are as defined above, X is a halogen and R' is a C₁ -C₆ alkyl group,with ammonia followed by acetic anhydride.

Compounds of formula (I') may be prepared by an analogous process whichcomprises treating a compound of formula (V'): ##STR26## wherein R₁ toR₅, X and R' are as defined above, with ammonia followed by aceticanhydride.

X in formula (V) or (V') is typically iodine. R' is, for example, a C₁-C₄ alkyl group such as a methyl, ethyl, propyl, i-propyl, butyl,sec-butyl or tert-butyl group.

A review of synthetic approaches to unsaturated 3-monosubstituted and3,6-disubstituted-2,5-piperazinediones is provided in Heterocycles,1983, 20, 1407 (C.Shin).

Compounds of formula (A) may be converted into pharmaceuticallyacceptable salts, and salts may be converted into the free compound, byconventional methods. Suitable salts include salts with pharmaceuticallyacceptable, inorganic or organic, bases, or pharmaceutically acceptableinorganic or organic acids. Examples of inorganic bases include ammoniaand carbonates, hydroxides and hydrogen carbonates of group I and groupII metals such as sodium, potassium, magnesium and calcium. Examples oforganic bases include aliphatic and aromatic amines such as methylamine,triethylamine, benzylamine, dibenzylamine or α- or β-phenylethylamine,and heterocyclic bases such as piperidine, 1-methylpiperidine andmorpholine. Examples of inorganic acids include hydrochloric acid,sulphuric acid and orthophosphoric acid. Examples of organic acidsinclude p-toluenesulphonic acid, methanesulphonic acid, mucic acid andbutan-1,4-dioic acid.

Compounds of formula (A) may also be converted into pharmaceuticallyacceptable esters. Suitable esters include branched or unbranched,saturated or unsaturated C₁ -C₆ alkyl esters, for example methyl, ethyland vinyl esters.

Cancer cells which exhibit multiple drug resistance, referred to as MDRcells, display a reduction in intracellular drug accumulation comparedwith the corresponding drug-sensitive cells. Studies using in vitroderived MDR cell lines have shown that MDR is often associated withincreased expression of a plasma membrane glycoprotein (P-gp) which hasdrug binding properties. P-gp is thought to function as an efflux pumpfor many hydrophobic compounds, and transfection studies using clonedP-gp have shown that its overexpression can confer the MDR phenotype oncells: see, for example, Ann. Rev. Biochem 58 137-171 (1989).

A major function of P-gp in normal tissues is to export intracellulartoxins from the cell. There is evidence to suggest that overexpressionof P-gp may play a clinical role in multiple drug resistance. Increasedlevels of P-gp mRNA or protein have been detected in many forms of humancancers--leukaemias, lymphomas, sarcomas and carcinomas. Indeed, in somecases P-gp levels have been found to increase in tumour biopsiesobtained after relapse from chemotherapy.

Inhibition of P-gp function in P-gp mediated MDR has been shown to leadto a net accumulation of anti-cancer agent in the cells. For example,Verapamil a known calcium channel blocker was shown to sensitise MDRcells to vinca alkaloids in vitro and in vivo: Cancer Res., 41,1967-1972 (1981). The proposed mechanism of action involves competitionwith the anti-cancer agent for binding to the P-gp. A range ofstructurally unrelated resistance-modifying agents acting by thismechanism have been described such as tamoxifen (Nolvadex:ICI) andrelated compounds, and cyclosporin A and derivatives.

Compounds of formula A and their pharmaceutically acceptable salts andesters (hereinafter referred to as "the present compounds") have beenfound in biological tests to have activity in modulating multiple drugresistance. The results are set out in Example 10 which follows. Thepresent compounds may therefore be used as multiple drug resistancemodifying agents, also termed resistance-modifying agents, or RMAs. Thepresent compounds can modulate, e.g. reduce, or eliminate multiple drugresistance. The present compounds can therefore be used in a method ofpotentiating the cytotoxicity of an agent which is cytotoxic to a tumourcell. Such a method comprises, for instance, administering one of thepresent compounds to the tumour cell whilst the tumour cell is exposedto the cytotoxic agent in question. The therapeutic effect of achemotherapeutic, or antineoplastic, agent may thus be enhanced. Themultiple drug resistance of a tumour cell to a cytotoxic agent duringchemotherapy may be reduced or eliminated.

The present compounds can also be used in a method of treating a diseasein which the pathogen concerned exhibits multi-drug resistance, forinstance multi-drug resistant forms of malaria (Plasmodium falciarum),tuberculosis, leishmaniasis and amoebic dysentery. Such a methodcomprises, for instance, administering one of the present compounds with(separately, simultaneously or sequentially) the drug to which thepathogen concerned exhibits multi-drug resistance. The therapeuticeffect of the drug may thus be enhanced.

A human or animal patient harbouring a tumour may be treated forresistance to a chemotherapeutic agent by a method comprising theadministration thereto of one of the present compounds. The presentcompound is administered in an amount effective to potentiate thecytotoxicity of the said chemotherapeutic agent. Examples ofchemotherapeutic or antineoplastic agents which are preferred in thecontext of the present invention include vinca alkaloids such asvincristine and vinblastine; anthracycline antibiotics such asdaunorubicin and doxorubicin; mitoxantrone; actinomycin D andplicamycin.

In addition, a human or animal patient suffering from a disease in whichthe responsible pathogen exhibits multi-drug resistance may be treatedfor resistance to a therapeutic agent by a method comprising theadministration thereto of one of the present compounds.

Examples of such disease include multi-drug resistant forms of malaria(Plasmodium falciparum), tuberculosis, leishmaniasis and amoebicdysentery.

MDR modulators also have utility in the delivery of drugs across theblood-brain barrier, and in the treatment of AIDS and AIDS-relatedcomplex. The present compounds can therefore be used in a method offacilitating the delivery of drugs across the blood brain barrier, andin the treatment of AIDS or AIDS-related complex. A human or animalpatient in need of such treatment may be treated by a method comprisingthe administration thereto of one of the present compounds.

The present compounds can be administered in a variety of dosage forms,for example orally such as in the form of tablets, capsules, sugar- orfilm-coated tablets, liquid solutions or suspensions or parenterally,for example intramuscularly, intravenously or subcutaneously. Thepresent compounds may therefore be given by injection or infusion.

The dosage depends on a variety of factors including the age, weight andcondition of the patient and the route of administration. Typically,however, the dosage adopted for each route of administration when acompound of the invention is administered alone to adult humans is 0.001to 10 mg/kg, most commonly in the range of 0.01 to 5 mg/kg, body weight.Such a dosage may be given, for example, from 1 to 5 times daily bybolus infusion, infusion over several hours and/or repeatedadministration.

A piperazine of formula (A) or a pharmaceutically acceptable salt orester thereof is formulated for use as a pharmaceutical or veterinarycomposition also comprising a pharmaceutically or veterinarilyacceptable carrier or diluent. The compositions are typically preparedfollowing conventional methods and are administered in apharmaceutically or veterinarily suitable form. An agent for use as amodulator of multiple drug resistance comprising any one of the presentcompounds is therefore provided.

For example, the solid oral forms may contain, together with the activecompound, diluents such as lactose, dextrose, saccharose, cellulose,corn starch or potato starch; lubricants such as silica, talc, stearicacid, magnesium or calcium stearate and/or polyethylene glycols; bindingagents such as starches, arabic gums, gelatin, methylcellulose,carboxymethylcellulose, or polyvinyl pyrrolidone; disintegrating agentssuch as starch, alginic acid, alginates or sodium starch glycolate;effervescing mixtures; dyestuffs, sweeteners; wetting agents such aslecithin, polysorbates, lauryl sulphates. Such preparations may bemanufactured in known manners, for example by means of mixing,granulating, tabletting, sugar coating, or film-coating processes.

Liquid dispersions for oral administration may be syrups, emulsions andsuspensions. The syrups may contain as carrier, for example, saccharoseor saccharose with glycerol and/or mannitol and/or sorbitol. Inparticular, a syrup for diabetic patients can contain as carriers onlyproducts, for example sorbitol, which do not metabolise to glucose orwhich only metabolise a very small amount to glucose. The suspensionsand the emulsions may contain as carrier, for example, a natural gum,agar, sodium alginate, pectin, methylcellulose, carboxymethylcelluloseor polyvinyl alcohol.

Suspensions or solutions for intramuscular injections may contain,together with the active compound, a pharmaceutically acceptable carriersuch as sterile water, olive oil, ethyl oleate, glycols such aspropylene glycol, and, if desired, a suitable amount of lidocainehydrochloride. Some of the present compounds are insoluble in water. Acompound may be encapsulated within liposomes.

The following Examples illustrate the invention:

REFERENCE EXAMPLE 1 Preparation of(3Z,6Z)-6-Benzylidene-3-(4-methoxybenzylidene)-2,5-5 piperazinedione (3)##STR27## 1,4-Diacetyl-2,5-piperazinedione (8)

1,4-Diacetyl-2,5-piperazinedione (8) was prepared by the publishedprocedure (S. M. Marcuccio and J. A. Elix, Aust. J. Chem., 1984, 37,1791).

(3z)-1-Acetyl-3-(4-methoxybenzylidene)-2,5-piperazinedione (9)

(3Z)-1-Acetyl-3-(4-methoxybenzylidene)-2,5-piperazinedione (9) wasprepared by the published procedure (T. Yokoi, LM. Yang, T. Yokoi, RY.Wu, and KH. Lee, J. Antibiot., 1988, 41, 494).

(3Z,6Z)-6-Benzylidene-3-(4-methoxybenzylidene)-2,5-piperazinedione (3)

A mixture of (3Z)-1-acetyl-3-(4-methoxybenzylidene)-2,5-piperazinedione(9) (1.0 g, 3.6 mmol), benzaldehyde (430 μl, 4.2 mmol) and triethylamine(1.14 ml), 8.2 mmol), in dry DMF (20 ml), was heated at 130° C. for 18h. The reaction mixture was cooled to room temperature and poured intoethyl acetate (100 ml). A yellow solid precipitated which was filteredoff and dried. Yield 360 mg (31%).

C₁₉ H₁₆ N₂ O₃

¹ H nmr (400 MHz d₆ -DMSO)

δ: 3.80 (3H, s, O--Me); 6.77 (1H, s, CH═C); 6.78 (1H, s, CH═C); 6.98(2H, d, J=8 Hz, 2×C--H on Ar--OMe); 7.30-7.56 (7H, m, Ph and 2×C--H onAr--OMe); 10.15 (2H, br.s, N--H).

¹³ C nmr (100 MHz d₆ -DMSO)

δ: 58.68; 117.66; 118.03; 118.77; 128.11; 128.92; 129.95; 131.53;132.11; 132.69; 134.44; 136.59; 161.39; 161.62; 162.71.

ms (desorption chemical ionisation, ammonia):

m/z (% relative intensity) : 321 (100) MH⁺.

ir : KBr (diffuse reflectance):

v max (cm⁻¹) : 1620, 1700, 3100, 3220.

Elemental analysis:

Calculated for C₁₉ H₁₆ N₂ O₃ : C 71.24, H 5.03, N 8.74.

Found: C 70.92, H 5.02, N 8.80. C 70.89, H 5.06, N 8.79%

REFERENCE EXAMPLE 2 Preparation of(3Z,6Z)-6-Benzylidene-3-(4-methoxybenzylidene)-2,5-piperazinedione (3)##STR28##

Compound 16 is treated with ammonia and subsequently with aceticanhydride to yield 1-acetyl-3-benzylidene-2,5-piperazinedione (18).

Compound 18 is then condensed, in the presence of caesium carbonate ortriethylamine in DMF, with 4-methoxybenzaldehyde to yield compound 3.

REFERENCE EXAMPLE 3 Preparation of1-acetyl-3-benzylidene-2,5-piperazinedione

1,4-Diacetyl-2,5-piperazinedione (25.0 g, 126 mmol), which is compound(8) mentioned in Reference Example 1, was heated at 120°-130° C. in DMF(200 ml) with triethylamine (17.6 ml, 126 mmol) and benzaldehyde (13.0ml, 126 mmol). After 4 h the mixture was cooled to room temperature andpoured into EtOAc (1000 ml), and washed three times with brine. Anysolid formed at this stage was filtered off. The filtrate was dried(MgSO₄) and the solvent removed in vacuo. The residue was recrystallisedfrom EtOAc:Hexane to give 11.78 g (38%) of the title compound as ayellow solid.

¹ H NMR (CDCl₃ 400 MHz) δ=2.69 (3H, s) 4.54 (2H, s) 7.20 (1H, s) 7.40(3H, m), 7.48 (2H, m), 7.93 (1H, br.s)

MS(DCI,NH₃): 262 (MNH₄ ⁺, 20%), 245 (MH⁺, 53%), 220 (52%), 204 (100%),203 (100%)

    ______________________________________    Microanalysis                C            H      N    ______________________________________    Calc        63.93        4.95   11.47    Found       64.11        5.02   11.41                64.05        4.90   11.44    ______________________________________

REFERENCE EXAMPLE 4 Preparation of1-acetyl-3-(4-acetamidobenzylidene)-2,5-piperazinedione

1,4-Diacetyl-2,5-piperazinedione (10.0 g, 50 mmol), prepared by thepublished procedure mentioned in Reference Example 1, was stirred in DMF(40 ml) with 4-acetamidobenzaldehyde (8.24 g, 50 mmol) and triethylamine(7 ml, 50 mmol) and heated to 120° C. After 2% h the mixture was cooledto room temperature, diluted with EtOAc (100 ml) and stirred overnight.The solid formed was collected, washed with EtOAc and dried to give 8.46g (56%) of a yellow solid.

¹ H NMR (CDCl₃ +CF₃ CO₂ H, 400 MHz) δ=2.32 (3H, s) 2.72 (3H, s) 4.68(2H, s) 7.36 (1H, s) 7.45 (2H, d, J=8 Hz) 7.60 (2H, d, J=8 Hz)

    ______________________________________    Microanalysis                C            H      N    ______________________________________    Calc        59.80        5.02   13.95    Found       60.08        5.09   13.89                60.11        5.07   13.86    ______________________________________

REFERENCE EXAMPLE 5 Preparation of(3Z)-1-acetyl-3-(4-methoxybenzylidene)-2,5-piperazinedione (9) and1-acetyl-3-(4-methoxybenzylidene)-4-methyl-2,5-piperazinedione (10)##STR29##

Compound 12 is treated with NH₃ to afford3-(4-methoxybenzylidene-2,5-piperazinedione (13). This is then treatedwith acetic anhydride to yield(3Z)-1-acetyl-3-(4-methoxybenzylidene-2,5-piperazinedione (9).

Compound 12 is treated with, as methylating agent, iodomethane in thepresence of potassium carbonate in dimethylformamide to give compound14. Compound 14 is then treated with NH₃ and subsequently with aceticanhydride to yield1-acetyl-3-(4-methoxybenzylidene)-4-methyl-2,5-piperazinedione (10).

REFERENCE EXAMPLE 6 Preparation of(3Z,6Z)-3-benzylidene-6-(4-methoxybenzylidene)-1-methyl-2,5-piperazinedione (1) ##STR30##(3Z)-1-Acetyl-3-(4-methoxybenzylidene)-4-methyl-2,5-piperazinedione (10)and 1-Acetyl-5-methoxy-3-(4-methoxybenzylidene)-3,6-dihydropyrazin-2-one(11)

A mixture of (3Z)-1-Acetyl-3-(4-methoxybenzylidene)-2,5-piperazinedione(9) (2.0 g, 7.3 mmol), methyl iodide (0.46 ml, 7.3 mmol), and sodiumcarbonate (800 mg, 7.5 mmol) in dry DMF (50 ml) was stirred under anatmosphere of dry nitrogen for 3 days. The reaction mixture was thenpoured into ethyl acetate (500 ml) and washed with water (4×100 ml) andbrine. The organic phase was separated, dried (MgSO₄), and the solventremoved in vacuo. The residue was purified by flash chromatography(silica, EtOAc:Hexane, 1:1) to give(3Z)-1-acetyl-3-(4-methoxybenzylidene)-4-methyl-2,5-piperazinedione (10)1.38 g (66%) as a yellow solid and1-acetyl-5-methoxy-3-(4-methoxybenzylidene)-3,6-dihydropyrazin-2-one(11) 248 mg (11.8%) as a bright yellow solid.

(3Z)-1-Acetyl-3-(4-methoxybenzylidene)-4-methyl-2,5-piperazinedione(10):

C₁₅ H₁₆ N₂ O₄

¹ H nmr (400 MHz CDCl₃):

δ: 2.63 (3H, s, Ac); 2.95 (3H, s, N--Me); 3.87 (3H, s, O--Me); 4.52 (s,2H, N--CH₂ --CO); 6.93 (2H, d, J=8 Hz, Aromatic); 7.26 (1H, s, C═CH);7.29 (2H, d, J=8 Hz), Aromatic).

ms (desorption chemical ionisation, ammonia):

m/z (% relative intensity): 306 (34%) MNH₄ ⁺ ; 289 (100%) 216 (14%)

ir : KBr (diffuse reflectance) v _(max) (cm⁻¹) : 1690, 1700, 3000.

Elemental analysis:

Calculated for C₁₅ H₁₆ N₂ O₄ : C 62.49, H 5.59, N 9.72 C 62.48, H 5.58,N 9.68. C 62.51, H 5.65, N 9.67%

1-Acetyl-5-methoxy-3-(4-methoxybenzylidene)-3,6-dihydropyrazin-2-one(11):

C₁₅ H₁₆ N₂ O₄

¹ H nmr (400 MHz CDCl₃)

δ: 2.68 (3H, s, Ac); 3.86 (3H, s, Ar--OMe); 3.99 (3H, s, O--Me); 4.44(s, 2H, N--CH₂ --CO); 6.95 (2H, d, J=8 Hz, Ar); 7.32 (1H, s, C═CH); 8.03(2H, d, J=8 Hz, Ar).

ms (desorption chemical ionisation, ammonia):

m/z (% relative intensity): 289 (100%) MH³⁰ ; 247 (14%)

ir : KBr (diffuse reflectance):

V _(max) (cm⁻¹) : 1610, 1690, 1700, 1740, 2950.

Elemental Analysis:

Calculated for C₁₅ H₁₆ N₂ O₄ : C 62.49, H 5.59, N 9.72. C 62.52, H 5.59,N 9.64. C 62.52, H 5.64, N 9.66%

(3Z,6Z)-3-Benzylidene-6-(4-methoxybenzylidene)-1-methyl-2,5-piperazinedione(1)

A mixture of(3Z)-1-Acetyl-3-(4-methoxybenzylidene)-4-methyl-2,5-piperazinedione (10)(200 mg, 0.69 mmol) and sodium hydride (60% dispersion in oil, 28 mg,0.69 mmol) in dry DMF (10 ml) was stirred at room temperature for 18 h.Benzaldehyde (71 μl, 0.69 mmol) was then added and the reaction mixturestirred at room temperature for 18 h. It was then diluted with ethylacetate (100 ml) and washed with brine (4×50 ml). The organic phase wasseparated, dried (MgSO₄), and the solvent removed in vacuo. The residuewas purified by flash chromatography (silica, dichloromethane containing1% MeOH) to give 48 mg (21 w) of a yellow solid.

C₂₀ H₁₈ N₂ O₃

¹ H nmr (400 MHz CDCl₃):

δ: 3.06 (3H, s, N--Me); 3.87 (3H, s, O--Me); 6.93 (2H, d, J=8 Hz, 2×C--Hon Ar--OMe); 7.06 (1H, s, Ph--CH═C); 7.23 (2H, d, J=8 Hz, 2×C--H onAr--OMe); 7.27 (1H, s, MeOAr--CH═C); 7.30-7.48 (5H, m, Ph); (1H, br.s,N--H).

¹³ C nmr (100 MHz CDCl₃)

δ: 36.62; 55.34; 113.86; 116.80; 121.30; 126.02; 126.14; 128.47; 128.78;129.06; 129.45; 131.11; 133.07; 159.66; 159.68; 159.95.

ms (desorption chemical ionisation, ammonia) : 335 (100%) MH⁺.

ir : KBr (diffuse reflectance) : v _(max) (cm⁻¹) : 1690, 3000, 3180,3400.

Elemental analysis:

Calculated for C₂₀ H₁₈ H₂ O₃ : 0 71.84, H 5.43, N 8.38. C 71.81, H 5.31,N 8.31. C 71.80, H 5.25, N 8.31%.

REFERENCE EXAMPLE 7 Preparation of(3Z,6Z)-3-benzylidene-6-(4-methoxybenzylidene)-1,4-dimethyl-2,5-piperazinedione(2) ##STR31##(3Z,6Z)-3-Benzylidene-6-(4-methoxybenzylidene)-1,4-dimethyl-25-piperazinedione (2)

A mixture of(3Z,6Z)-3-Benzylidene-6-(4-methoxybenzylidene)-2,5-piperazinedione (3)(0.5 g, 1.56 mmol), sodium hydride (60% dispersion in mineral oil, 125mg, 3.1 mmol) and methyl iodide (243 μl, 3.9 mmol) in dry DMF (50 ml)was stirred at room temperature for 4 days. The solvent was then removedin vacuo and the residue purified by flash chromatography (silica,eluting with EtOAc:Hexane, 1:3) to give 220 mg (40%) of compound 2 as ayellow solid.

C₂₁ H₂₀ N₂ O₃

¹ H nmr (400 MHz CDCl₃)

δ: 2.95 (3H, s, N--Me); 3.04 (3H, s, N--Me); 3.85 (3H, s, O--Me); 6.90(2H, d, J=8 Hz, 2×C--H on Ar--OMe); 7.19 (1H, s, CH═C); 7.21 (1H, s,CH═C) 7.30-7.56 (7H, m, Ph and 2×C--H on Ar--OMe).

ms (desorption chemical ionisation, ammonia) :

m/z (% relative intensity): 349 (100) MH⁺.

EXAMPLE 1 Preparation of 1894

1-acetyl-3-benzylidene-2,5-piperazinedione, prepared as described inReference Example 3, was treated with the aldehyde formed by thereaction between indole-3-carboxaldehyde and di-tert-butyldicarbonate inacetonitrile in the presence of Et₃ N (1 equivalent) and DMAP (0.1equivalent) at room temperature for 72 hours; the reaction was performedin DMF in the presence of Cs₂ CO₃ (1.1 equivalent) at 90° C. for 2hours. The resulting compound was recrystallised from ethylacetate togive compound 1894 in 27% yield.

EXAMPLE 2 Preparation of 1896

Compound 1894 prepared as described in Example 1, was alkylated withmethyl iodide (5 equivalents) in THF in the presence of sodium hydride(1.1 equivalent) at room temperature for 18 hours, to give compound 1800in 88% yield.

Subsequent treatment of 1800 with excess TFA, in dichloromethane for 18hours gave compound 1896 in 47% yield.

EXAMPLE 3 Preparation of Further Compounds of the Invention

Compound 1896, prepared as described in Example 2, was converted intofurther compounds of formula A using the following reagents andconditions:

(a) Treatment with sodium hydride (1.1 equivalent) andbenzylchloroformate (3 equivalents) in DMSO at room temperature for 2hours gave compound 1940 in 48% yield.

(b) Treatment of 1896 with bromomethylphthalimide (2 equivalents) andsodium hydride (1.1 equivalents) in THF with a few drops of DMF at roomtemperature for 72 hours gave compound 1897 in 72% yield.

(c) Treatment of 1896 with methyl bromoacetate (3 equivalents) andsodium hydride (1.1. equivalent) in DMSO at room temperature for 24hours gave compound 1941 in 39% yield.

(d) Treatment of 1896 with t-butyl bromoacetate (3 equivalents) andsodium hydride (2 equivalents) in DMSO at room temperature for 18 hoursgave compound 1942 in 18% yield.

(e) Treatment of 1896 with bromopropylphthalimide (3 equivalents) andsodium hydride (2 equivalents) in DMSO at 60° C. for 2 hours gavecompound 1943 which was subsequently purified by column chromatographyusing SiO₂ /20-40% EtOAc in hexane. Compound 1943 was obtained in 15%yield.

EXAMPLE 4 Preparation of 1895

Compound 1894, prepared as described in Example 1, was treated with3-bromopropylphthalimide and sodium hydride (1.1. equivalents) in DMF atroom temperature to give compound 1895 in 62% yield.

EXAMPLE 5 Preparation of 1938

1-acetyl-3-benzylidene-2,5-piperazinedione, prepared as described inReference Example 3, was treated with 4-dimethylaminocinnamaldehyde andCs₂ CO₃ in DMF at 80° C. for 4 hours. The product of that reaction(1921) was treated first with sodium hydride in DMF for 10 minutes andthen with methyliodide (3 equivalents) for 4 hours. The product waspurified by column chromatography (silica, EtOAc/hexane) to yield 1938in 25% yield.

EXAMPLE 6 Preparation of 1937

1-acetyl-3-benzylidene-2,5-piperazinedione, prepared as described inReference Example 3, was treated with β-phenylcinnamaldehyde in DMF inthe presence of Cs₂ CO₃ at 80° C. The product of that reaction (1922)was recrystallised from acetic acid. It was then treated first withsodium hydride (2.5 equivalents) in DMF for 10 minutes, followed byiodomethane (3 equivalents) for 4 hours. The product was purified bycolumn chromatography on silica to give 1937.

EXAMPLE 7 Preparation of 1933

1-acetyl-3-benzylidene-4-methyl-2,5-piperazinedione was treated withcyclohexanecarboxaldehyde (4 equivalents) in the presence of potassiumt-butoxide (2 equivalents) in t-butanol and DMF at 100° C. for 90minutes. The product was recrystallised from ethyl acetate/hexane togive compound 1933 in 29% yield.

EXAMPLE 8 Preparation of Further Compounds A

Further compounds of the invention may be prepared in accordance withthe method described in Example 5 as follows. The starting material1-acetyl-3-benzylidene-2,5-piperazinedione (a compound of generalformula I in which Y is a phenyl ring) is replaced by the appropriatecompound of formula (I) in which Y has the definition desired in thefinal product; this starting material may be prepared by reacting1,4-diacetyl-2,5-piperazinedione, prepared as described in ReferenceExample 1, with the appropriate aldehyde Y--CHO.

The desired starting material of formula (I) thus produced is reactedwith the appropriate substituted aldehyde (of formula X--CHO wherein Xhas the definition desired in the final product) and the remainder ofthe reaction is the performed as described in Example 5. The followingcompounds can be prepared in this manner: 1875, 1873, 1836, 1834, 1877,1799, 1777 and 1871.

Similarly, the process described in Example 1 may be used to prepareother compounds of formula A in which R₁₄ is methyl and R₁₅ is hydrogen,by the use of appropriately substituted aldehydes Y--CHO and X--CHO. Thefollowing compounds may be prepared in this way: 1563, 1564, 1565, 1569,1596, 1597 and 1641.

EXAMPLE 9 Pharmaceutical Composition

Tablets, each weighing 0.15 g and containing 25 mg of a compound of theinvention can be manufactured as follows:

Composition for 10,000 tablets

compound of the invention (250 g)

lactose (800 g)

corn starch (415 g)

talc powder (30 g)

magnesium stearate (5 g)

The compound of the invention, lactose and half of the corn starch aremixed. The mixture is then forced through a sieve 0.5 mm mesh size. Cornstarch (10 g) is suspended in warm water (90 ml). The resulting paste isused to granulate the powder. The granulate is dried and broken up intosmall fragments on a sieve of 1.4 mm mesh size. The remaining quantityof starch, talc and magnesium stearate is added, carefully mixed andprocessed into tablets.

EXAMPLE 10 Testing of compounds A as modulators of MDR

Materials and Methods

The EMT6 mouse mammary carcinoma cell line and the MDR resistant sublineAR 1.0 were cultured in RPMI 1640 medium containing 10% foetal calfserum and 2mM glutamine at 37° C. in 5% CO₂. Cells were passaged between1 in 200 and 1 in 2000 in the case of the parental cell line and between1 in 20 and 1 in 200 in the case of the MDR resistant subline, aftertrypsinisation (0.25% trypsin, 0.2 gl⁻¹, EDTA).

1. Drug accumulation assay

AR 1.0 cells were seeded into 96 well opaque culture plates (CanberraPackard). The assay medium contained a mixture of tritiated Daunorubicin(DNR), a cytotoxic agent, and unlabelled DNR (0.25μ Ci/ml; 2 μM).Compounds of formula A were serially diluted in assay medium over arange of concentrations from 100 nM to 100 μM. The cells were incubatedat 37° C. for 1 hr before washing and counting of cell associatedradioactivity. Each assay included a titration of the known resistancemodifying agent Verapamil as positive control. Results were expressed as% maximum accumulation where 100% accumulation is that observed in thepresence of 100 μM Verapamil.

The results are set out in the following Table

    ______________________________________                 IC50 (μm)                            MAX accumulation    Compound No. Accumulation                            (% 100 μm VRP)    ______________________________________    1563         --         32.9    1564         --         46.3    1565         --         37.3    1569         --         46.0    1596         --         47.7    1597         50.0       59.1    1641         --         50.5    1777         80.0       50.0    1799         --         40.0    1800          7.0       --    1834          5.0       --    1836         --         14.0    1839         20.0       --    1840         12.0       --    1871          6.0       --    1873          5.0       56.0    1874         10.0       --    1875          5.0       --    1877         20.0       --    1880          7.0       --    1894         --         36.0    1895         --         12.0    1896         12.0       --    1897          3.0       --    1940         10.0       --    1941         10.0       --    1942         10.0       --    1943         10.0       --    1932         10.0       --    1934          1.0       --    1935          6.0       --    ______________________________________

2. Potentiation of Doxorubicin toxicity

Compounds of formula A were examined for their ability to potentiate thetoxicity of doxorubicin in AR 1.0 cells. In initial proliferation assayscompounds were titrated against a fixed concentration of doxorubicin(0.5-1 μM) which alone is non-toxic to AR 1.0 cells. Incubations withdoxorubicin were over a four day period before quantitation ofproliferation using the calorimetric sulphorhodamine B assay (Skehan etal; J. Natl. Cancer Inst. 82 pp 1107-1112 (1990)).

Compounds which were shown to be able to sensitise AR 1.0 cells to0.8-1.7 μM doxorubicin without high innate toxicity were selected forfurther study. Cells were cultured for four days with concentrations ofdoxorubicin over the range of 0.5 nM-50 μM in the presence of Verapramilat its maximum subtoxic level determined from previous experiments.Proliferation was quantified as described by Skehan et al, loc cit. TheIC₅₀ (concentration required to reduce proliferation to 50% of theuntreated controls) for doxorubicin alone and with the Verapamil werederived and used to calculate the potentiation index (PI):

    ______________________________________     ##STR32##                             Potentiation    Compound No. Conc Comp μM                             Index (at 5 μM)    ______________________________________    1800         5           40    1834         3               30 (3 μm)    1839         3               15 (3 μm)    1871         5           20    1874         5           20    1897         5           75    1940         5           14    1941         5            4    1942         5           20    1943         5           20    ______________________________________

                  TABLE 3    ______________________________________                                      TOXICITY                                      WITH                           COMPOUND   CYTOTOXIC    COMPOUND CONC CYTOTOXIC                           TOXICITY   AGENT    NO.      AGENT (μg/ml)                           (IC50 μM)                                      (IC 50 μM)    ______________________________________    1597     1.00          25.0       6.0    1641     1.00          --         0.0    1800     1.00          10.0       0.8    1834     0.50          10.0       0.8    1839     0.50          30.0       1.5    1840     0.50           5.0       1.0    1871     0.50          40.0       1.0    1873     0.50           8.0       0.8    1875     0.50          10.0       0.8    1880     0.50          10.0       1.0    1896     0.50          30.0       4.0    1897     0.50          50.0       1.5    1940     0.50           7.0       0.7    1941     0.50          50.0       1.5    1942     0.50          15.0       0.7    1943     0.50          60.0       0.2    ______________________________________

EXAMPLE 11 Characterization of Compounds of Formula A

The compounds of Formula A were characterised by conventional massspectorscopic, microanalytical, proton NMR and infra-red techniques. Theresults are set out in Table

    __________________________________________________________________________                   Mass spec .sup.1 H nmr                   m/z, mass Solvent    Mol. Formula   intensity δ    Microanalysis    No.  (M. Wt)   (mode)    all 400 MHz   Calc    Found    __________________________________________________________________________    XR1943         C.sub.3 H.sub.28 N.sub.4 O.sub.4                   545 57% MH+                             CDCl.sub.3         544       417 8%    2.29(2H, p),                   358 13%   2.99(3H, s),                   206 45%   3.16(3H s),                   CI NH.sub.3                             3.78(2H, t),                             4.25(2H, t),                             7.21-7.41                             (overlapping solvent                             & multiple sample                             signals),                             7.43(1H, s),                             7.68(1H, d),                             7.73(2H, m),                             7.86(2H, m)    XR1942         C.sub.28 H.sub.29 O.sub.4 N.sub.3                   471 37% M+                             CDCl.sub.3         471       415 100%  1.46(9H, s),                   357 26%   2.99(3H, s),                   213 12%   3.15(3H, s),                   168 28%   4.78(2H, s),                   116 22%   7.19-7.47                   89 8%     (overlapping solvent                   EI+       & multiple sample                             signals),                             7.69(1H, d).    XR1941         C.sub.25 H.sub.23 O.sub.4 N.sub.3                   430 100% MH+                             CDCl.sub.3         429       CI NH.sub.3                             3.00(3H, s),                             3.15(3H, s),                             3.79(3H, s),                             4.90(2H, s),                             7.19-7.45                             (overlapping solvent                             and multiple sample                             signals).                             7.72(1H, d)    XR1940         C.sub.30 H.sub.25 N.sub.3 O.sub.4                   492.59 15% MH+,                             CDCl.sub.3 C  73.31                                               73.03                                                   73.06         491       358.47 50%,                             3.0(3H, s),                                        H  5.13                                               5.16                                                   5.17         (491.547).                   217.37 10%                             3.08(3H, s),                                        N  8.55                                               8.46                                                   8.41                   169.23 27%                             5.50(2H, s),                   CI NH.sub.3                             7.25-7.48                             (overlapping solvent                             & sample peaks),                             7.51(2H, d),                             7.60(1H d),                             7.65(1H, s),                             8.21(1H, d).    XR1897         C.sub.31 H.sub.24 O.sub.4 N.sub.4                   516 100% M+                             CDCl.sub.3         516       356 20%   2.94(3H, s),                   160 100%  3.14(3H, s),                   116 22%   6.00(2H, s),                   77 15%    7.21-7.28                   EI+       (overlapping solvent                             and sample peaks),                             7.30-7.42(7H, c),                             7.59(1H, s),                             7.65(1H, d),                             7.75(2H, m),                             7.88(3H, c).    XR1896         C.sub.22 H.sub.19 O.sub.2 N.sub.3                   357 100% M+                             CDCl.sub.3         357       155 34%   2.99(3H, s),                   116 13%   3.12(3H, s),                   EI+       7.20(multiple                             signals & solvent),                             7.69(1H, d),                             8.56(1H, br, s).    XR1895         C.sub.37 H.sub.34 N.sub.4 O.sub.6                   630 1% M+ CDCl.sub.3 C  70.46                                               69.90                                                   69.77         630       530 20%   1.67(9H, s),                                        H  5.43                                               5.47                                                   5.48                   188 100%  2.33(2H, m),                                        N  8.88                                               8.98                                                   8.93                   160 39%   2.98(3H, s),                   41 41%    3.98(2H, t),                   EI+       4.59(2H, t),                             6.82(1H, s),                             7.19(1H, d),                             7.27-7.39(7H, c),                             7.53(3H, overlapping                             signals),                             7.76(1H, m),                             7.82(1H, d),                             8.19(1H, d),                             8.53(1H, s).    XR1894         C.sub.26 H.sub.25                   NO SPECTRUM                             CDCl.sub.3 C  70.41                                               70.23                                                   70.22                   OBSERVED CI                             1.71(9H, s),                                        H  5.68                                               5.62                                                   5.61                   NO SPECTRUM                             3.03(3H, s),                                        N  9.47                                               9.45                                                   9.47                   OBSERVED FAB+                             7.17(1H, s),                   443 30%   7.28(8H, c),                   387 18%   7.68(1H, d),                   315 7%    7.35                   132 28%                   91 15%                   57 100%                   EI+    XR1875         C.sub.25 H.sub.25 N.sub.3 O.sub.5                   448 100%  CDCl.sub.3         447       DCI NH.sub.3                             1.69(9H, s),                             3.05(3H, s),                             3.19(3H, s),                             6.49(1H, s),                             7.06(1H, s),                             7.28-7.33                             (overlapping solvent                             & sample signal),                             7.38(1H, t),                             7.49(1H, s),                             7.54-7.61(3H, c),                             8.16(1H, d).    XR1873         C.sub.27 H.sub.25 N.sub.3 O.sub.4 Cl.sub.2                   526 14%   CDCl.sub.3 C  61.60                                               61.30                                                   61.38                   469 18%   1.70(9H, s),                                        H  4.79                                               4.72                                                   4.71                   434 39%   2.82(3H, s),                                        N  7.98                                               7.99                                                   8.00                   426 100%  3.08(3H, s),                             7.10(1H, s),                             7.21-7.46                             (overlapping solvent                             & sample signals),                             7.57(1H, d),                             7.65(1H, s),                             8.18(1H, d).    XR1836         C.sub.18 H.sub.16 N.sub.2 O.sub.3                   MH+ 309   CDCl.sub.3 C         308       DCI NH.sub.3                             7.58(1H, s),                                        H                             7.48(1H, s),                                        N                             7.35(H,),                             7.20(2H, s),                             7.05(1H, s),                             6.45(1H, s),                             3.18(3H, s),                             2.95(3H, s).    XR1834         C.sub.25 H.sub.25 N.sub.3 O.sub.4 S                   464 44%   CDCl.sub.3 C  64.78                                               64.53                                                   64.56         463       402 81%   1.69(9H, s),                                        H  5.44                                               5.49                                                   5.42                   363 100%  3.06(3H, s),                                        N  9.06                                               8.95                                                   8.94                   DCI NH.sub.3                             3.20(3H, s),                             7.09-7.13(2H, m),                             7.28-7.32(2H, m),                             7.39(1H, t),                             7.46(1H, d),                             7.57(1H, d),                             7.60(1H, s),                             8.17(1H, d).    XR1563         C.sub.18 H.sub.16 N.sub.2 O.sub.4                   325 100%  CDCl.sub.3 C  66.66                                               66.40                                                   66.11         324       DCI NH.sub.3                             3.05(3H, s),                                        H  4.97                                               4.91                                                   4.94                             3.87(3H, s),                                        N  8.64                                               8.60                                                   8.50                             6.61(1H, broad s),                             6.88(1H, s),                             6.92(2H, d),                             7.22-7.28                             (overlapping solvent                             & sample signals),                             7.55(1H, brs),                             7.74(1H, s),                             7.78(1H, V.brs).    XR1564         C.sub.18 H.sub.16 N.sub.2 O.sub.3 S                   341 100%  CDCl.sub.3 C  63.51                                               63.39                                                   63.36         340       DCI NH.sub.3                             3.06(3H, s),                                        H  4.74                                               4.73                                                   4.74                             3.85(3H, s),                                        N  8.23                                               8.19                                                   8.16                             6.91(2H, d),                                        S  9.42                                               9.31                                                   9.42                             7.13-7.30                             (overlapping solvent                             & sample signals),                             7.49(1H, d),                             7.99(1H, V.brs).    XR1565         C.sub.27 H.sub.27 N.sub.3 O.sub.5                   474 100%  CDCl.sub.3 C  68.49                                               68.04                                                   67.74         473       374 80%   1.71(9H, s),                                        H  5.75                                               5.64                                                   5.61                   DCI NH.sub.3                             3.08(3H, s),                                        N  8.87                                               8.90                                                   8.81                             3.87(3H, s),                             6.92(2H, d),                             7.16(1H, s),                             7.25-7.28                             (overlapping solvent                             & sample signal),                             7.35(1H, t),                             7.41(1H, t),                             7.69(1H, d),                             7.86(1H, s),                             8.01(1H, s),                             8.19(1H, s).    XR1569         C.sub.17 H.sub.14 N.sub.2 O.sub.2 S                   328 (M+NH.sub.4, 8%),                             CDCl.sub.3         MW = 310  311 (MH+, 100%)                             3.20(3H, s),                   DCI NH.sub.3                             7.04-7.10(3H, m),                             7.30(1H, s),                             7.35-7.48(6H, m),                             8.13(1H, brs).    XR1596         C.sub.18 H.sub.16 O.sub.4 N.sub.2                   325 (100%)                             CDCl.sub.3 C  66.66                                               66.61                                                   66.71         324       DCI NH.sub.3                             3.21(3H, s),                                        H  4.97                                               4.90                                                   4.97                             3.85(3H, s),                                        N  8.64                                               8.56                                                   8.57                             6.45(1H, s),                             6.95-7.01(3H,                             overlapping signals),                             7.06(1H, s),                             7.35(2H, d),                             7.45(1H, fine m),                             7.52(1H, brs),                             7.90(1H, V.brs).    XR1597         C.sub.18 H.sub.16 O.sub.3 N.sub.2 S                   341 (100%)                             CDCl.sub.3 C  63.51                                               63.68                                                   63.71         340       DCI NH.sub.3                             3.19(3H, s),                                        H  4.74                                               4.79                                                   4.69                             3.85(3H, s),                                        N  8.23                                               8.22                                                   8.21                             6.95-7.10(5H,                                        S  9.42                                               9.35                                                   9.29                             multiple signals),                             7.29(1H, s),                             7.36(2H, d),                             7.43(1H, d),                             7.94(1H, V.brs).    XR1840         C.sub.24 H.sub.20 N.sub.3 O.sub.2 Cl                   417 (M+, 1%),                             CDCl.sub.3                   383 (34%),                             4.85(2H, s),                   382 (100%)                             6.93(3H, m),                   DCI NH.sub.3                             7.20(3H, m),                             7.22-7.50(H, m),                             8.00(2H, d, J=4Hz),                             8.77(2H, d, J=4Hz),                             10.52(1H, brs).    XR1641         C.sub.17 H.sub.14 N.sub.2 O.sub.2 S                   328 (M.sup.+ NH.sub.4, 4%)                             CDCl.sub.3 C  65.79                                               65.72                                                   65.77         MW = 310  311 (MH+, 100%)                             3.10(3H, s),                                        H  4.55                                               4.53                                                   4.53                   DCI NH.sub.3                             7.07(1H, s),                                        N  9.03                                               9.02                                                   9.02                             7.08(1H, d),                             7.20-7.48(8H, m),                             7.94(1H, brs).    XR1839         C.sub.24 H.sub.19 N.sub.3 O.sub.2                   382 (MH+, 100%).                             CDCl.sub.3                   DCI NH.sub.3                             4.85(2H, s),                             6.89(2H, m),                             6.95(1H, s),                             7.20(3H, m),                             7.22-7.50(8H, m),                             7.91(1H, brs),                             8.68(2H, d, J=5Hz)    XR1874         C.sub.34 H.sub.33 N.sub.3 O.sub.5                   564 29%   CDCl.sub.3 C  72.45                                               72.03                                                   71.87         563       507 25%   1.71(9H, s),                                        H  5.90                                               5.88                                                   5.90                   463 100%  3.00(3H, s),                                        N  7.46                                               7.27                                                   7.24                             3.83(3H, s),                             4.82(2H, s),                             6.90(2H, d),                             7.00(2H, m),                             7.15-7.22(4H,                             (multiple signals),                             7.25-7.42                             (overlapping solvent                             & sample signlas),                             7.57(1H, d),                             7.71(1H, s),                             8.20(1H, d).    XR1877         C.sub.18 H.sub.15 N.sub.3 O.sub.4 S                   370 100%  CDCl.sub.3         369       387 86%   2.85(3H, s),                   DCI NH.sub.3                             3.19(3H, s),                             7.06-7.13(2H, m),                             7.32(1H, s),                             7.35(2H, d),                             7.41(1H, s),                             7.47(1H, m),                             7.53(1H, t),                             7.66(1H, t),                             8.16(1H, d).    XR1799         C.sub.22 H.sub.19 N.sub.3 O.sub.2                   309 MH.sup.+  (100%)                             CDCl.sub.3                   CI NH.sub.3                             7.47(1H, s),                             7.32-7.18(5H, m),                             7.13(1H, s),                             6.93(1H, s),                             6.52(1H, d),                             6.43(1H, q),                             3.22(3H, s),                             2.88(3H, s).    XR1800         C.sub.27 H.sub.27 N.sub.3 O.sub.4                   458 MH.sup.+  (100%)                             CDCl.sub.3 C  70.88                                               70.74                                                   70.67                   CI NH.sub.3                             8.16(1H, d),                                        H  5.95                                               6.05                                                   6.02                             7.62(1H, s),                                        N  9.18                                               9.05                                                   8.99                             7.58(1H, d),                             7.42-7.23(9H, m),                             3.07(3H, s),                             3.0(3H, s),                             1.69(9H, s).    XR1880         C.sub.25 H.sub.22 N.sub.2 O.sub.4                   415 100%  CDCl.sub.3         414       DCI NH.sub.3                             2.94(3H, s),                             3.82(3H, s),                             4.93(2H, s),                             6.57(1H, s),                             6.89(2H, d),                             7.02(1H, s),                             7.09(2H, m),                             7.12(1H, s),                             7.21-7.28                             (overlapping sample &                             solvent),                             7.53(1H, s),                             7.66(1H, s).    XR1777         C.sub.23 H.sub.22 N.sub.2 O.sub.3                   MH+ (100%) 375                             CDCl.sub.3 C  73.78                                               73.38                                                   73.40         374       376 (30%), 374                             7.48-6.88(13H, m),                                        H  5.92                                               5.85                                                   5.94                   (30%).    3.85(3H, s),                                        N  7.48                                               7.43                                                   7.39                   DCI NH.sub.3                             3.52(3H, s),                             3.00(3H, s).    XR1871         C.sub.20 H.sub.24 N.sub.2 O.sub.2                             CDCl.sub.3 C  74.05                                               73.83                                                   73.73         324                 7.40-7.26(5H, m),                                        H  7.46                                               7.40                                                   7.37                             7.15(1H, d),                                        N  8.63                                               8.61                                                   8.58                             6.05(1H, d),                             3.37(3H, s),                             2.89(3H, s),                             2.48(1H, m),                             1.85-1.70(5H, m),                             1.35-1.22(5H, m).    XR1938         C.sub.24 H.sub.25 N.sub.3 O.sub.2                   MH+ (100%) 388                             CDCl.sub.3         387       CI NH.sub.3                             7.52-7.22(7H, m),                             7.18(1H, s),                             6.90(1H, s),                             6.85(2H, m),                             6.68(2H, d),                             3.50(3H, s),                             3.00(6H, s),                             2.92(3H, s).    XR1932         C.sub.28 H.sub.24 N.sub.2 O.sub.2                   MH+ (100%) 421                             CDCl.sub.3         420       CI NH.sub.3                             7.45-7.28(15H, m),                             7.20(1H, s),                             6.95(1H, d),                             6.84(1H, d),                             3.55(3H, s),                             2.89(3H, s).    XR1933         C.sub.19 H.sub.22 N.sub.2 O.sub.2                   MH+ (100%) 311                             CDCl.sub.3         310       CI NH.sub.3                             8.06(1H, brs),                             7.40-7.23(6H, m),                             6.05(1H, d),                             2.95(3H, s),                             2.22(1H, m),                             1.85-1.68(4H, m),                             1.45-1.21(6H, m).    1935 C.sub.30 H.sub.25 N.sub.3 O.sub.4 = 491                   mH.sup.+ (45%)-492                             CDCl.sub.3                   Also (40%)-305,                             8.02(d, 2H),                   188-(100%)                             7.57-7.50(m, 2H),                   CI/NH.sub.3                             7.38-7.25(m, 7H),                             7.22(d, 2H),                             7.06(m, 1H),                             6.91(d, 1H),                             6.78(s, 1H),                             4.56(t, 2H),                             3.98(t, 2H),                             2.95(s, 3H),                             2.35(quintet, 2H)    1934 C.sub.26 H.sub.25 N.sub.3 O.sub.4 = 443                   mH.sup.+ (20%)-444                             CDCl.sub.3 400mH.sub.2                                        C  70.41                                               70.29                                                   70.41                   Also (100%)-140                             8.05(d, 2H),                                        H  5.68                                               5.71                                                   5.68                   CI/NH.sub.3                             7.45-7.28(m, 9H),                                        N  9.47                                               9.38                                                   9.38                             6.92(s, 1H),                             4.45(t, 2H),                             3.76(t, 2H),                             2.98(s, 3H),                             2.68(s, 4H),                             2.20(quintet, 2H).    1932 C.sub.26 H.sub.25 N.sub.3 O.sub.4 = 443                   mH.sup.+ (100%)-444                             7.41-7.32(m, 10H),                   Also 352(10%),                             7.22(s, 1H),                   317(30%), 7.19(s, 1H),                   140(90%)  3.60(t, 2H),                   CI/NH.sub.3                             3.30(t, 2H),                             3.02(s, 3H),                             2.56(s, 4H),                             1.72(quintet, 2H).    __________________________________________________________________________

We claim:
 1. A compound selected from the group consisting of adiketopiperazine of formula (Aa): ##STR33## wherein R₁₄ is H or C₁ -C₆alkyl optionally substituted by phenyl;R₁₅ is H or C₁ -C₆ alkyloptionally substituted by an N-phthalimidyl, N-succinimidyl or oxo ordioxo-indolinyl group; and one of X and Y is a phenyl ring which isunsubstituted or substituted by one or more substituents selected fromhalogen, C₁ -C₆ alkoxy, --NO₂ and NR₁₁ R₁₂ wherein R₁₁ and R₁₂ are each,independently, H or C₁ -C₆ alkyl; and the other is a heterocyclic ringselected from the group consisting of furan thiophene, pyridine andindole, the indole ring being optionally N-substituted byphthalimidyl-C₁ -C₆ -alkyl, succinimidyl-C₁ -C₆ -alkyl, oxo- ordioxo-indolenyl, --(CH₂)_(n) COOR₁₁ or --(CH₂)_(n) COOCH₂ Ph wherein R₁₁is H or C₁ -C₆ alkyl and n is 0, 1 or 2, a cyclohexyl group or a group--CH═CHPh or --CH═C(Ph)₂ ; with the proviso that at least one of R₁₄ andR₁₅ is other than hydrogen; pharmaceutically acceptable salts thereofand pharmaceutically acceptable esters thereof selected from branchedand unbranched, saturated and unsaturated C₁ -C₆ alkyl esters.
 2. Acompound according to claim 1 wherein, when X or Y is a heterocyclicring, it is selected from 4-pyridyl, furan-2-yl, furan-3-yl,thiophen-2-yl thiophen-3-yl and optionally N-substituted indol-3-ylgroups.
 3. A compound according to claim 1 selectedfrom:(3Z,6Z)-6-Benzylidene-1-methyl-3-(1-tert-butoxycarbonyl-3-indolyl)methylene-2,5-piperazinedione;(3Z,6Z)-1-Benzyl-6-benzylidene-3-(4-pyridyl)methylene-2,5-piperazinedione;(3Z,6Z)-1,4-Dimethyl-3-(1-tert-butoxycarbonyl-3-indolyl)methylene-6-(2-thienylidene)-2,5-piperazinedione;(3Z,6Z)-1-Benzyl-6-benzylidene-3-(4-pyridyl)methylene-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-1,4-dimethyl-6-(1-tert-butoxycarbonyl-3-indolyl)methylene-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene- I ,4-dimethyl-6- i-(3-phthalimidopropyl)-3-indolyl!methylene-2 ,5-piperazinedione;(3Z,6Z)-3-Benzylidene-6-(1-methoxycarbonyl-3-indolyl)methylene-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-6-(1-benzyloxycarbonyl-3-indolyl)methylene-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-1,4-dimethyl-6-(γ-phenylcinnamylidene)-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-1,4-dimethyl-6-(1-tert-butoxycarbonyl-3-indolyl)methylene-2,5-piperazinedione;(3Z)-3-Benzylidene-1,4-dimethyl-6-(2-oxo-3-indolinylidene)-2,5-piperazinedione;(3Z,6Z)-6-(3-furylmethylene)-3-(4-methoxybenzylidene-1-methyl-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-6-(4-dimethylaminocinnamylidene)-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-6-Benzylidene-3-cyclohexylmethylene-1-methyl-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-6-(2-furyl)methylene-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-6-(3-indolyl)methylene-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-3-(4-Methoxybenzylidene)-1-methyl-6-(2-thienylmethylene)-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-1-methyl-6-(3-thienylmethylene)-2,5-piperazinedione;(3Z)-3-Benzylidene-1,4-dimethyl-6-(1-methyl-2-oxo-3-indolinylidene)-2,5-piperazinedione;(3Z,6Z)-6-(4-Methoxybenzylidene)-1-methyl-3-(1-tert-butoxycarbonyl-3-indolyl)methylene-2,5-piperazinedione;(3Z,6Z)-3-Cinnamylidene-6-(4-methoxybenzylidene)-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-6-Benzylidene-3-(2-furylidene)-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-6-cyclohexylmethylene-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-6-(2,6-dichlorobenzylidene)-3-(1-tertbutoxycarbonyl-3-indolyl)methylene-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-4-benzyl-3-(1-tertbutoxycarbonyl-3-indolyl)methylene-6-(4-methoxybenzylidene)-1-methyl-2,5-piperazinedione;(3Z,6Z)-6-(3-furylmethylene)-6-(1-tertbutoxycarbonyl-3-indolyl)methylene-1,4-dimethyl-2,5-piperazinedione;(3Z,6Z)-1,4-dimethyl-6-(2-nitrobenzylidene)-3-(2-thienylmethylene)-2,5-piperazinedione;(3Z,6Z)-4-Benzyl-3-(3-furylmethylene)-6-(4-methoxybenzylidene)-1-methyl-2,5-piperazinedione;(3Z,6Z)-3-(3-Furylmethylene)-6-(4-methoxybenzylidene)-1-methyl-2,5-piperazinedione;(3Z,6Z)-6-(4-Methoxybenzylidene)-1-methyl-3-(2-thienylmethylene)-2,5-piperazinedione;(3Z,6Z)-3-Benzylidene-1-methyl-6-(2-thienylmethylene)-2,5-piperazinedione,and the pharmaceutically acceptable salts thereof.
 4. A pharmaceuticalor veterinary composition comprising a pharmaceutically or veterinarilyacceptable carrier or diluent and, as an active principle, a compound asclaimed in claim
 1. 5. A method of treating resistance to ananthracycline antibiotic which has antineoplastic activity in a patientharbouring a tumour, which method comprises administering to a patientin need thereof a therapeutically effective amount of a compound asdefined in claim
 1. 6. A method according to claim 5 wherein theanthracycline antibiotic is doxorubicin or daunorubicin.
 7. A methodaccording to claim 5 which comprises administering the said compound tothe patient while the tumour is exposed to the said anthracyclineantibiotic.
 8. A process for preparing a compound as defined in claim 1,the process comprising:(a) condensing a compound of formula (I):##STR34## wherein R₁₅ and Y are as defined in claim 1 and are optionallyprotected, with a compound of formula (II): ##STR35## wherein X is asdefined in claim 1 and is optionally protected, in the presence of abase in an organic solvent thereby obtaining a compound of formula Aa inwhich R₁₄ is hydrogen; or (b) condensing a compound of formula (I'):##STR36## wherein R₁₄ and X are as defined in claim 1 and are optionallyprotected with a compound of formula (III): ##STR37## wherein Y is asdefined in claim 1 and is optionally protected, in the presence of abase in an organic solvent; and (c) if desired, converting the resultingcompound of formula Aa in which R₁₄ or R₁₅, respectively, is hydrogeninto a corresponding compound of formula Aa in which R₁₄, R₁₅,respectively, is a C₁ -C₆ alkyl group, by treatment with an alkylatingagent of formula R₁₄ --X or R₁₅ --X wherein R₁₄ and R₁₅ are as definedin claim 1 and X is a halogen; and/or, if required, removing optionallypresent protecting groups, or, if desired, converting a compound offormula Aa in which R₁₅ is hydrogen into a compound of formula Aawherein R₁₆ is C₁ -C₆ alkyl optionally substituted as defined in claim1, by treatment with an alkylating agent of formula R₁₆ --X wherein R₁₆is as defined in claim 1 and X is a halogen; and/or if required,removing optionally present protecting group, if desired, converting acompound of formula Aa into a pharmaceutically acceptable salt or esterthereof, and/or, if desired, converting a salt or ester into a freecompound.
 9. A compound selected from the group consisting of adiketopiperazine of formula (Ab): ##STR38## wherein R₁₄ is H or C₁ -C₆alkyl optionally substituted by phenyl;R₁₆ is C₁ -C₆ alkyl optionallysubstituted by an N-phthalimidyl, N-succinimidyl or oxo- ordioxo-indolinyl group; X and Y, which may be the same or different, areindependently selected from(i) a heterocyclic ring selected from furan,thiophen, pyridine and indole, the indole ring being optionallyN-substituted by phthalimidyl-C₁ -C₆ -alkyl, succinimidyl-C₁ -C₆ -alkyl,oxo- or dioxo-indolinyl, --(CH₂)_(n) COOR₁₁ or --(CH₂)_(n) COOCH₂ Ph,wherein R₁₁ is H or C₁ -C₆ alkyl and n is 0, 1 or 2; (ii) a phenyl ringwhich is unsubstituted or substituted by one or more substituentsselected from halogen, C₁ -C₆ alkoxy, --NO₂ and NR₁₁ R₁₂ wherein R₁₁ andR₁₂ are each, independently, H or C₁ -C₆ alkyl; (iii) a cyclohexylgroup; and (iv) a group --CH═C(R₁₇ Ar); R₁₇ is H or optionallysubstituted phenyl and Ar is optionally substituted phenyl, the optionalsubstituent on the phenyl ring in each case being selected from halogen,--NO₂, --N(R₁₁ R₁₂) wherein R₁₁ and R₁₂ are as defined above and C₁ -C₆alkoxy; pharmaceutically acceptable salts thereof and pharmaceuticallyacceptable esters thereof selected from branched and unbranched,saturated and unsaturated C₁ -C₆ alkyl esters; with the proviso that Xand Y are not both a phenyl ring as defined above under (ii).
 10. Acompound according to claim 9 wherein one of X and Y is an unsubstitutedor substituted phenyl ring and the other is a heterocyclic ring, acyclohexyl group or a group --CH═CHPh or --CH═C(Ph)₂.
 11. A compoundaccording to claim 9 wherein, when X or Y is a heterocyclic ring, it isselected from 4-pyridyl, furan-2-yl, furan-3-yl, thiophen-2-yl,thiophen-3-yl and optionally N-substituted indol-3-yl groups.
 12. Acompound according to claim 9 which is selected from the groupconsistingof:(3Z,6Z)-6-Benzylidene-1-methyl-5-(3-phthalimidopropoxy)-3-(1-tert-butoxycarbonyl-3-indolyl)methylene-3,6-dihydro-2-pyrazinone;and(3Z,6Z)-6-Benzylidene-5-methoxy-3-(2-thienylidene)-3,6-dihydro-2(1H)-pyrazinone;and the pharmaceutically acceptable salts thereof.
 13. A pharmaceuticalor veterinary composition comprising a pharmaceutically or veterinarilyacceptable carrier or diluent and, as an active principle, a compound asclaimed in claim
 9. 14. A method of treating resistance to ananthracycline antibiotic which has antineoplastic activity in a patientharbouring a tumour, which method comprises administering to a patientin need thereof a therapeutically effective amount of a compound asdefined in claim
 9. 15. A method according to claim 14 wherein theanthracycline antibiotic is doxorubicin or daunorubicin.
 16. A methodaccording to claim 14 which comprises administering the said compound tothe patient while the tumour is exposed to the said anthracyclineantibiotic.